Mewing is a form of oral posture training purported to improve jaw and facial structure. It was named after Mike and John Mew, the controversial British orthodontists who created the technique as a part of a practice called "orthotropics". It involves placing one's tongue at the roof of the mouth and applying pressure, with the aim of changing the structure of the jaws. No credible scientific research has ever proven the efficacy of orthotropics.

Many orthodontists believe that mewing lacks evidence as a viable alternative treatment to orthognathic surgery. Mike Mew was expelled from the British Orthodontic Society, and faces a misconduct hearing for posing harm to child patients who underwent his treatments. While Mike Mew has disparaged traditional orthodontics, his orthotropic treatments for young children cost £12,500 for 36 months, and involve the wearing of headgear, neckgear, and expansion appliances in the mouth.

According to maxillofacial surgeon Paul Coceancig, "Mewing and chewing offer no structural change to the jaw, or other health benefits", adding: "Will chewing a bone help your dog grow a bigger jaw?". Since 2019, mewing has received widespread media coverage due to its virality on social media, especially in incel and looksmaxxing subcultures. Data from Google Trends indicates an increase in global interest and popularity for "Mewing" starting from January 2019. According to a 2024 article in The Independent, some school teachers say that students gesture to their jawline to indicate that they are mewing and do not wish to answer questions.